Given the detrimental effects associated with problematic internet use (PIU) and the need to better understand its nature and evolution, the present study examined the development of PIU in a sample of 1,750 adolescents (aged 16–19) from Finland over a 3‐year period. We documented the social (loneliness, perceived maternal and paternal behaviors) and individual (sex) antecedents, as well as the outcome implications (depressive symptoms, substance use, academic achievement) of PIU trajectories. Outcomes also predicted PIU trajectories. Latent curve modeling revealed an initially moderate, and subsequently decreasing trajectory of PIU. PIU was predicted by loneliness, paternal neglect, maternal care, depressive symptoms, and being male. In turn, PIU trajectories predicted increases in depressive symptoms and substance use, but decreases in academic achievement.